In the article titled, “Explosives Detection Technology Basics,” Campus Safety shared ways that hospitals, schools and universities can use technology to develop a multi-layered approach to detect explosives on campuses. Now, find out which technologies are the best to implement.
X-Rays
When someone walks through a body scanner or a package is sent through an X-ray baggage screener, complex software algorithms, based on chemistry, help operators identify the material based on its atomic number. Additionally, they can determine whether it is organic, inorganic or overlapping. How is this done? When an object passes through the screener, generator(s) produce its X-ray beam, a detector board sees that X-ray and then a computer processes the image, taking many variables into consideration. This subsequently gives an operator an output image to evaluate. This all happens quickly.
When multiple X-ray generators are used, better image characterization is achieved. For example, if you put three people in a row and take one photo, from the top down, you might end up with limited detail, such as the color of their hair. This is similar to what you gather from a single-view x-ray machine. But a camera on top, and one on the sides or in the front as well, gives a much more complete and accurate picture.
In much the same way, two or more X-ray generators give a much more complete picture, including an object’s density, volume and atomic number. The atomic number of an element is directly proportional to its density. When an X-ray goes through something, the more dense the object, the less X-ray goes through it. Denser materials look different. So, for example, since a piece of paper is organic, it will appear light orange; an item containing aluminum appears green; and steel will show up as blue. All of this information increases accuracy, reduces the occurrence of false alarms and decreases the amount of time it takes to determine if an object is a threat.
In an environment where ingested contraband can also pose a threat, full body X-ray scanners like the B-SCAN are a valuable tool and an alternative to highly invasive searches that are timely and subject security personnel to risk when they conduct them. Full-body scanners can increase safety, reduce cost and improve efficiency.
Ion Mobility Spectrometer
Another explosives detection technology sensitive enough to detect parts per billion of material is ion mobility spectrometry (IMS). IMS works by introducing an electrical charge to tested molecules and then pushing them through a drift tube. The time that it takes those molecules to reach the end of the tube – its drift time – reveals its atomic number. A larger molecule will be slower than a smaller one for example.
This technology is very sensitive; it can measure particles that are smaller than nano-grams, or down to one one-billionth of a gram. Because of this ability to test even tiny amounts of residue, screening locations like airport checkpoints and air cargo facilities use systems that allow swabs of hands, suitcase handles and other locations that might have been touched by the suspicious material to be analyzed. Particles from 50 grams of an explosive device hidden nearby or recently handled will have a small chance of escaping this detection process, because even extensive cleaning might not rid a person or object of all of the traceable residue particles.
These technologies come in desktop or portable versions, and the later versions typically run off batteries. No matter the size, they detect a wide range of threats depending on the customer’s need.
Raman Spectroscopy
Raman spectroscopy is a technique that uses a laser beam directed onto a sample to identify unknown materials based on their molecular structure. The single frequency (or wavelength) of the laser beam is scattered into different frequencies by the atoms and molecules that make up matter. The resulting Raman scattering is detected via a CCD detector. This information is processed by an integrated computer to generate a “Raman spectrum,” a graphical representation of the intensity of the scattered light as a function of its frequencies.
The Raman spectrum can be analyzed by sophisticated chemometric software and ultimately compared against Raman spectra stored in software libraries. Algorithms are used to assess how well the spectrum of the unknown sample matches that of those stored within the libraries and report the library hit. Mixture analysis algorithms enable the reporting of up to two components in a solid or liquid mixture.
At the heart of some systems, such as Smith Detection’s ACE-ID, is Orbital Raster Scanning (ORS) technology. The laser beam, reflected off a moving mirror, traces a ring pattern on the sample. Currently fielded Raman products generate a fixed focal point on the sample from the stationary laser beam. ACE-ID’s configuration produces a toroidal shaped pattern rather than the fixed focal point generated by a stationary beam. The moving beam over the sample has been shown to lower the probability of sample heating and bleaching. This limits the chances of heating a fixed spot in the sample and igniting energetic materials. Reducing laser heating can also improve the probability of identification of samples. Moreover, scanning the laser interrogates larger areas providing more representative Raman signatures over non-uniform samples while maintaining signal-to-noise ratios comparable to stationary laser systems. As an added safety measure, the ORS is interlocked with the laser excitation source to prevent illuminating the sample with a stationary laser.
